Wednesday, December 29, 2021

Preparation and standardization of 0.1 N potassium dichromate

Learn about the preparation and standardization of 0.1 N potassium dichromate solution through a laboratory experiment or practical.

Aim:

To prepare and standardize 0.1 N potassium dichromate solution using standard sodium chloride (volumetric solution).

Requirements:

Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.

Chemicals: Potassium dichromate (K2Cr2O7), potassium iodide (KI), hydrochloric acid (HCL), sodium thiosulphate (Na2S2O3), and starch solution, etc.

Preparation of 0.1N potassium dichromate solution:

Take properly weighed 06.00 gm of potassium dichromate (It should be previously dried at 120C for 4 hours and cool in a desiccator) and add in 100 ml of distilled water, Once it has completely dissolved, make up the volume to 1000 ml with water.

Titration procedure:

  • All glassware should be cleaned and dried according to standard laboratory procedures.
  • Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
  • Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
  • Remove air bubbles from the burette and adjust the reading to zero.
  • Take 40.00 ml of water and add 40.00 ml of prepared potassium dichromate solution in a stoppered flask.
  • Add 03.00 gm of potassium iodide and 05.00 ml of HCl.
  • Stopper the flask immediately, swirl to ensure even mixing, and then let stand for 10 minutes in the dark.
  • Rinse the stopper and interior walls of the flask with water, and titrate with freshly standardized 0.1N sodium thiosulphate solution until the solution becomes yellowish green.
  • Add 02.00 ml starch solution and continue the titration until the blue color disappears.
  • To get accurate results, repeat the titration three times.
  • Properly record the readings of the burette.
  • Take their mean and calculate the normality of the potassium dichromate solution.
  • 1 ml of 0.1 M sodium thiosulphate is equivalent to 0.0049 g of potassium dichromate.

Observation table:

Sr. No.

Content in conical flask

 

Burette reading

Volume of titrant used (ml)

Initial

Final

1

 

 

 

 

2

 

 

 

3

 

 

 

 

Mean:


Calculation:


A = B X C / D

Where,

A =normality of K2Cr2O7 solution
B = Na2S2O3 solution (ml) required for titration
C = Normality Na2S2O3 solution
D = K2Cr2O7 solution used


Result:


The strength of the prepared potassium dichromate solution was found to be_____N.


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